Weigh feeding apparatus

ABSTRACT

Disclosed herein is an automatically controlled weigh feeding apparatus including a container for prefilling with a substance, a device for discharging the substance from the container at a controllable rate, apparatus for weighing the substance being discharged and for producing an electrical signal proportional to that weight, a voltage to frequency converter connected to receive the electrical signals, a digital computer, apparatus coupled to an output of the voltage to frequency converter for inputting data signals to the digital computer, the computer being adapted to compute a corrective signal based on the input data signals received, and coupling apparatus coupled between the computer and the device for discharging the substance from the container for controlling the rate of discharge responsive to the corrective signal.

This is a continuation of application Ser. No. 907,960, Filed May 22,1978, .Iadd.now abandoned, .Iaddend.which is a continuation of Ser. No.748,397, Dec. 7, 1976 now U.S. Pat. No. 4,111,272.

BACKGROUND OF THE INVENTION

This invention relates to feeding systems and it is particularlyapplicable to apparatus for feeding fluid-like material. Systemsconstructed according to the present invention are particularly adapted,among other possible uses, for accurately feeding a wide variety ofsubstances including dry materials regardless of whether the material isfree-flowing, sluggish, or pressure sensitive; and ranging fromamorphous powders to flakes, pellets, chunks and even fibers, as well asliquids.

Various control weigh feeding systems have been known in the past, asfor example, the system disclosed in U.S. Patent Application Ser. No.345,587, filed Mar. 28, 1973, which has issued as U.S. Pat. No.3,889,848. In accordance with this application, there is provided aweigh feeding apparatus wherein the discharge rate of a fluid substancefrom a container is maintained at a predetermined constant value. Thecontainer and its contents are weighted, and an electrical signal isproduced which signal has an amplitude proportional to the weight of thecontainer and its contents. This electrical signal, which varies as thecontents of the container are discharged, is differentiated and appliedto a comparator circuit together with a reference signal, wherefore theoutput of the comparator circuit may be used to control said dischargerate of the substance as it is fed from the container. The comparatoroutput is applied to a signal generator for producing a motor drivesignal for a DC motor having its output shaft connected to drive adevice for discharging the substance from the container. The signalgenerator may comprise a pulsing circuit for controlling a pair of SCR'swhich are disposed in a rectifying bridge circuit connected between anAC voltage source and the input of the DC motor. Accordingly, the speedof the motor is controlled by the pulsing circuit, which, in turn, iscontrolled by the algebraic sum of the output signal of a tachometergenerator which is coupled directly to the motor shaft, and outputsignal from the comparator. It can be stated that the above describedapparatus provides an accurate weigh feeding system, whereby the feedingrate may be maintained at a constant value, and wherein thepredetermined feeding rate may be adjusted by adjusting the value of thereference signal source.

Additionally, the output of the weighing device may be applied to a pairof differential amplifier circuits, along with a pair .[.or.]. .Iadd.of.Iaddend.reference voltage inputs, for determining when the contents ofthe container varies above and below desired maximum and minimum filllevels for the container. That is, circuitry is provided forautomatically refilling the container when the weight of the substancetherein reaches the desired minimum weight, and for terminating thefilling process for the container when the fluid substance thereinreaches the desired maximum weight. Such circuitry includes means formaintaining the discharge rate of the container at a constant rate equalto the instantaneous rate thereof immediately preceding energization ofthe filling device for the container. Particularly, the pair ofdifferential amplifier circuits are coupled to a pair of relay drivercircuits for controlling a relay circuit to energize the filling devicewhen the substance in the container reaches the minimum weight, and formaintaining that filling device in an energized state until thecontainer is refilled to its maximum desired level. The relay circuit isalso coupled to the comparator circuit, for controlling the latter toproduce a constant output during the refilling process for thecontainer, thereby maintaining the discharge rate of the container atthe value of the particular discharge rate thereof immediately precedingenergization of the filling device.

As pointed out in said U.S. Pat. No. 3,889,848 in certain installationsthere exists a possibility of physical forces impinging upon the weighfeeder from an external source, such as wind or air currents, physicalcontact with the weigh feeder by operating personnel, or the like, forexample. These forces cause the weigh feeder to move at a rate that isother than that resulting from the linear discharge of the contents ofthe container. Because such additional movement, i.e. acceleration, isan error and has no direct relationship to the actual discharge ofmaterial from the container, the control system could continue toperform its corrective function utilizing the erroneous output signalfor comparison with the fixed set point reference signal derivative. Theaforementioned patent discloses one means for preventing such excessiveand adnormal movements of the weigh feeder scale from grossly affectingor disturbing the normal operation of the system to thereby preventlarge excursions of the output feed rate.

Disclosed in our patent application, Ser. No. 678,391, which has issuedas U.S. Pat. No. 4,054,784, in one form thereof, is a new and improvedweigh feeding apparatus characterized by a container for a prefilledsubstance having means for discharging the substance therefrom at acontrollable rate. A scale system is provided for weighing the containerprefilled with the substance and an electrical circuit serves to producea first electrical signal proportional in amplitude to the weight, and ahigh gain amplifier amplifies the electrical signal. An analog-digitalconverter (ADC) is coupled to the amplifier and a digital computer isadapted to receive pulse signals from the ADC for computing andoutputting a signal corresponding to the signal received. Digital-analogconverter ramp offset means which is controlled by the computer outputsa controlled stepping signal, that is applied as a second input to theamplifier means to algebraically combine therewith. Each stepcorresponds to one time cycle of operation, thereby maintaining theoutput of the amplifier in a given preselected range of amplitude duringone time cycle of operation. The digital computer as another operationthereof computes a corrective signal based on the signals received, andmeans coupled between the computer and the means for discharging thesubstance from the container, serve to control the rate of dischargeresponsive to the corrective signal.

SUMMARY OF THE INVENTION

The present invention is directed to new, improved means foraccomplishing the foregoing objectives, as well as additionalobjectives, as will become apparent as the description proceeds.

One of the features of the present invention resides in the provision ofa new and improved weigh feeder system, which is capable of controllingmore operating parameters, which operates faster, which provides afaster responsive action, and which is more accurate as compared to theprior art systems. In addition, the feeder system of the presentinvention has a memory and is capable of taking into account past errorsin the material flow rate and taking corrective action with respectthereto.

Also, the system is capable of disregarding single or multipleextraneous material flow rate readings, which may be caused by suchfactors as noise, vibations, or the like, for example.

To the accomplishment of the foregoing and other objectives, theinvention contemplates the provision of a new and improved weigh feederapparatus, which comprises a container for prefilling with a substance,and means for discharging the substance from the container at acontrollable rate. Means are provided for weighing the substance beingdischarged, and means coupled thereto serve to produce electricalsignals proportional in amplitude to the weight determined. A voltage tofrequency converter, which receives the electrical signals, is coupledby electrical circuitry to a digital computer for inputting data signalsthereto. The digital computer is adapted to compute a corrective signalbased on the input data signals received, and means are coupled betweenthe computer and the means for discharging the substance from thecontainer for controlling the rate of discharge responsive to thecorrective signal.

In one form of the invention, the means for weighing the substance beingdischarged comprises a scale for weighing the container prefilled withthe substance, and in another form thereof the means for weighing thesubstance being discharged comprises a moving belt conveyor wherein theentire belt and its contents are weighed. In a third form the means fordischarging the substance comprises a volumetric type auger feederwherein the entire auger feeder and its contents are weighed.

According to one aspect of the invention, the weighing means areconnected to the voltage to frequency converter by a linear variabledifferential transformer and a differential DC amplifier circuit.

In one embodiment of the invention, the means coupled to an output ofthe voltage to frequency converter for inputting data signals to thedigital computer includes a first gating circuit, means coupling thisgating circuit to the voltage to frequency converter, and a secondgating circuit with an oscillator coupled thereto. A first logic circuitis provided for receiving information from the computer for selecting apredetermined time base period, and means are provided for coupling thislogic circuit to the gating circuits for enabling them. A first counteris connected to the output of the first gating circuit and a secondcounter is coupled to the output of the second gating circuit. A secondlogic circuit is provided for receiving information from the computerfor selecting a predetermined number of periods to be passed through thefirst gating circuit. A comparator is interposed between the firstcounter and the second logic circuit for determing when the firstcounter has counted the predetermined number of periods. A bit datalatch or register is connected to an output of the second counter, andmeans responsive to the comparator are provided for enabling the bitdata latch to receive bits of data from the second counter and todisenable the gating circuits and to reset the first and second countersthe counter means. In addition, means are provided for connecting anoutput of the bit data latch to the digital computer. According to anaspect of the invention, the means coupling the first logic circuit tothe gating circuits for enabling these circuits includes a time basegenerator driven by the oscillator.

Further, in a form thereof, the invention includes means for inputtinginto the digital computer a preselected feed rate. The computer hasprogrammed therein a calculation time cycle and is adapted to store inmemory a series of data signals received for each calculation time cycleand computing the corrective signal by comparing the signals receivedwith the preselected feed rate. The computer is adapted to maintain saidcorrective signal constant during the time when a preselected number ofthe signals received exceeds preselected upper of lower limits duringone calculation time cycle. Further, the computer is provided with meansfor correcting the data signals received to compensate for errors due toextraneous noise.

In still another form of the invention, the digital computer is adaptedto store in memory a series of data signals received for each of thecalculation time cycles and to compute the slope of the actual feed lineduring each such calculation time cycle. It also compares the computedslope during each time cycle with the computed slope for the lastpreceeding calculation time cycle, and determines the percentagevariation therefrom, and if the variation is within a predeterminedrange it proceeds to compute the corrective signal corresponding to thevariation, and if the variation is in excess of the predetermined rangeit maintains the corrective signal constant.

According to another aspect of the invention, there is providedunder-weight limit input means and over-weight input means to thedigital computer, and the computer is adapted to actuate an alarm whenthe data signals received by the computer exceed one of said limits. Thecomputer may also be adapted to integrate the preselected feed rate withrespect to time and output a display corresponding to the desired totalfeed commanded, and to integrate the actual total weight of material fedas determined by the data signals received and, by comparing said totalfeed commanded to the actual weight of material fed, adjust saidcorrective signal.

In accordance with other forms of the invention, means are provided foroperating the system in a volumetric mode, and means are provided forautomatically refilling the supply container to maintain the supply ofmaterial therein within preselected upper and lower limits.

These features of the invention have been outlined in order that thedetailed description thereof that follows may be better understood, andin order that the present contribution to the art may be betterappreciated. There are, of course, additional features of the inventionthat will be described more fully hereinafter. Those skilled in the artwill appreciate that the conception on which this disclosure is basedmay readily be utilized as the basis of the designing of otherstructures for carrying out the various purposes of the invention. It isimportant, therefore, that this disclosure be regarded as including suchequivalent constructions and methods as do not depart from the spiritand scope of the invention.

Several embodiments of the invention have been chosen for purposes ofillustration and description, and are shown in the accompanying drawingsforming a part of the specification, wherein:

FIG. 1 is a schematic side elevation and block diagram of a weigh feederassembly according to one embodiment of the invention;

FIG. 2 is a schematic side elevation and block diagram similar to FIG.1, but showing another embodiment of a weigh feeder assembly;

FIG. 3 is a schematic side elevation and block diagram similar to FIGS.1 and 2, but showing still another embodiment of a weigh feederassembly;

FIGS. 4A and 4B cooperate to form a block diagram of the interfacecircuitry for coupling any one of the feeder assemblies of FIGS. 1 to 3to a computer or micro processor;

FIG. 5 is a block diagram of the inputs and outputs of the computer ormicro processor according to the invention;

FIG. 6 is a graphic representation of the output voltage which respectto time of the differential amplifier circuit of the present invention;

FIG. 7 is a graphic representation of the actual measured feed curve ascompared to the desired feed curve, using the feeder assembly of FIG. 1;

FIG. 8 is a graphic representation of the positional relationship of theshaft encoder with respect to the system noise;

FIG. 9 is a graphic representation of the output of the voltage tofrequency converter with respect to time, before it is corrected for theinduced system noise;

FIG. 10 is a graphic representation of the output of the voltage tofrequency converter with respect to time, after it has been correctedfor the induced system noise;

FIG. 11 is a graphic representation of the actual measured feed curve ascompared to the desired feed curve similar to FIG. 7, but illustratinganother mode of programming the computer;

FIG. 12 is a graphic representation of the actual measured feed curve ascompared to the desired feed curve using the feeder assemblies of either.[.FIG. 1 or FIG. 2.]. .Iadd.FIG. 2 or FIG. 3.Iaddend.;

FIG. 13 is a flow chart showing the program start;

FIG. 14 is a flow chart of the background;

FIG. 15 is a flow chart of the timer routine of the computer;

FIG. 16 is a flow chart of the keyboard interrupts;

FIG. 17 is a flow chart of the calculation routine;

FIG. 18 is a flow chart for computing the scale weight and hopper level;and

FIG. 19 is a chart specifying the subroutine description.

In the embodiment of the invention shown in FIG. 1, there is illustrateddiagrammatically a feeder assembly indicated generally at 10, whichcomprises a container 12 with a discharge device connected thereto forfeeding a substance 14 from the container through a discharge conduit16. As illustrated, a variable speed DC motor 18, connected to agear-reduction device 20, is provided for driving the discharge device.The feeder assembly may comprise an auger mechanism as disclosed indetail in U.S. Pat. No. 3,186,602 issued June 1, 1965. The entirefeeding assembly, including the container, the discharge device, themotor, and the gear-reduction device is mounted on a scale 22, which maycomprise a structure as described in detail in U.S. Pat. No. 3,494,507,issued Feb. 10, 1970.

In accordance with the invention, there is provided a detecting device,as for example, a linear variable differential transformer (LVDT) 24,coupled to the scale for providing an electrical signal having anamplitude which is proportional to the weight of the container and itscontents. That is, as the contents of the container 12 are discharged, arelative movement occurs between the windings and the core of the LVDT,thereby causing a varying output voltage proportional to the varyingweight of the container and its contents. Thus, as the substance isdischarged from the container, the LVDT provides an electrical signalwhich varies in response to such discharge, which may, for example, be aDC voltage with a range of the order of from about plus or minus 3 voltsto about plus or minus 6 volts when the material in the container dropsfrom its upper level to its lower level.

In the embodiment of the invention illustrated in FIG. 2, there isprovided a feeder assembly indicated generally at 10 which comprises avolumetric type feeder 26 having an upper inlet 28 for receivingmaterial to be processed and a lower dispensing outlet 30 for dispensingthe material 32 onto a conveyor belt 34. A variable speed DC motor 35 isprovided for driving the discharge device. A suitable type of volumetricfeeder for this purpose is described in detail in the aforesaid U.S.Pat. No. 3,186,602.

The conveyor belt 34 is carried by a pair of spaced rollers 36, one ofwhich is driven by drive means, such as a constant speed motor and chaindrive, for example (not shown). The rollers are mounted on a conveyorsupport frame, not shown. In operation the material 32 passes from thefeeder 26 through the outlet 30 to the conveyor belt 34 and isdischarged therefrom as at 40 into a receiving hopper or container 42.Suitable scale means for the conveyor belt are described in detail inthe aforesaid U.S. Pat. No. 3,494,507. Thus, the conveyor belt 34 ismounted in such a manner that the entire belt and its contents can be"sensed" or weighed by a force sensing load cell, such as the LVDT 24,described hereinbefore in connection with the embodiment of FIG. 1.

In the embodiment of the invention illustrated in FIG. 3, there isprovided a feeder assembly indicated generally at 10, which alsocomprises a volumetric auger type feeder 44, having an upper inlet 46for receiving material to be processed and a lower enclosed dispensingoutlet 48. A particularly suitable type of volumetric feeder for thispurpose is described in detail in the aforesaid U.S. Pat. No. 3,186,602.The feeder 44 employs an auger (not shown) driven by a motor 50 forpropelling the material through the outlet 48 into a downspout 52, asindicated by arrow 54. The dispensing outlet and the downspout aremounted in fixedly sealed relationship with respect to each other. Thedownspout leads to the inlet of an enclosed auger type conveyor 56,which incorporates an auger 58 having a drive shaft 60 driven atsubstantially constant speed by a motor, not shown, through a chain andpulley system 62. The auger 58 serves to move the material through aconveyor cylinder 64 to a fixedly mounted discharge outlet 66 where itpasses into a discharge conduit 68, as indicated by arrow 70. Themovable conveyor cylinder 64 is flexibly connected in sealedrelationship to the fixed downspout 52, as by means of a downspoutsleeve 72. In addition, the movable cylinder .[.63.]. .Iadd.64.Iaddend.is flexibly connected in sealed relationship to the fixeddischarged conduit 68, by means of a sleeve clamping assembly 74.Accordingly, it will be appreciated that the material being processedpasses through a completely closed system from inlet to outlet. Aparticularly suitable system of this type is described in detail in U.S.Pat. No. 3,804,298 issued Apr. 16, 1974. The conveyor 64 is mounted in ascale-like manner so that the entire conveyor assembly and its contents,but not including conduits 48 or 68, or the equipment feeding thoseconduits, can be "sensed" or weighed by a force sensing load cell, suchas the LVDT 24, described hereinbefore in connection with the embodimentof FIG. 1.

In the embodiments illustrated in FIGS. 1, 2 and 3, the feederassemblies 10, having containers and discharge conduits for all types ofsubstances, are particularly suitable for solid particles, but it is tobe understood that the combinations described above may also be used forcontrolling the discharge of liquid substances from the containers,wherefore the augers would be replaced by pumps.

Referring next to FIGS. 4A and 4B, there is shown interface circuitryfor coupling the feeder assembly 10 to a micro processor and memory orcomputer 76. It will be appreciated that any one of the feederassemblies 10 of the embodiments of FIGS. 1-3 may be employed with thisinterface. The LVDT 24, FIG. 4A, is provided with a rod 78, which ismovable in response to the weight being measured. A sine wave oscillator80, which may, for example, comprise a Burr-Brown Model No. 8692-1001,has outputs 82 and 84 which are coupled to inputs 86 and 88 of the LVDTfor applying an AC input thereto. The LVDT has outputs 90 and 92, theoutput 90 being coupled to an input 94 of a differential DC amplifiercircuit 96 and the output 92 being connected to a summing junction 98which, in turn, is connected to an input 100 of the differential DCamplifier circuit 96. Also, applied to the summing junction 98 is anoffset circuit 102 controlled by an offset adjust 103. In addition, theamplifier circuit 96 is provided with a gain adjust 106. In theembodiments illustrated, the LVDT signal, which is a DC signal betweenabout minus 3 and plus 3 volts depending on the position of the movablerod 78, is fed into the differential DC amplifier 96 along with theoffset voltage. The offset adjust and the gain adjust set the output 104from the amplifier circuit for plus 5 volts when the portion of thefeeder system 10 mounted on the scale is empty and for plus 10 voltswhen the feeder system is full, as shown in FIG. 6. Any suitableamplifier circuit may be employed such as two Model OPO5EJ units, asmanufactured by Precision Monolithics, Inc. for example. The first unitis a differential amplifier circuit, which is followed by a variablegain single-ended amplifier circuit. The output 104 of the amplifiercircuit 96 is coupled to an input 108 of a voltage to frequencyconverter 110, which outputs a corresponding pulse train output at 112of from 5 KHz to 10 KHz. It will be appreciated that the embodiment ofFIG. 1 is a weight loss system wherein the weight on the scale as sensedby the LVDT gradually diminishes until the container 12 is empty, andthus the pulse train output gradually moves from 10 KHz to 5 KHz. On theother hand, in the embodiments of FIGS. 2 and 3, the weight on the scaleas sensed by the LVDT remains substantially constant so that the outputof the voltage to frequency converter 110 also remains constant. Thatis, if the frequency outputted is at 5 KHz then the rate of flow wouldbe zero, and if the frequency is 10 KHz then the rate of flow would bemaximum. In normal operation, the frequency outputted would be at asubstantially constant value somewhere therebetween, such as at 6 KHz,for example. The voltage to frequency converter may be a Burr-BrownModel VFC12, for example. The pulse train is fed to the input 114 of anoptical isolator 116 which may comprise, for example, a MonsantoCorporation Model No. MCL600. The optical isolator 116 outputs to adifferential line driver 118, which drives a twisted pair cable 120. Thepulse train is received by a differential line receiver 122 coupled tothe twisted pair cable.

A 10 MHz. crystal oscillator, or clock, 124 has an output 126 coupled toan input 128 of a time base generator 130 for driving the time basegenerator. Conword I circuit 132, which includes logic circuitry, has aninput 134 for receiving programmed information from the computer 76 andan output 136 coupled to an input 138 of the time base generator forselecting a particular time base period, and responsive thereto the timebase generator generates a selected time period, i.e. 1, 0.5, 0.25, or0.125 seconds the start of which is gated by a signal from the 10 MHzoscillator. This time base generator has an output 140 which is coupledto a start input 142 of gating circuit I, indicated at 144, and to startinput 146 of gating circuit II, indicated at 148, so that when the timebase generator generates a new period the gating circuits I and II areenabled. The output 140 of the time base generator is also coupled tothe real time clock of the computer 76, via line 141. The output 126 ofthe crystal oscillator 124 is coupled to an input 150 of the gatingcircuit II, which has an output 152 coupled to an input 154 (FIG. 4B) ofa high speed 24 bit counter 156. The differential line receiver 122 hasan output 158 coupled to an input 160 of the gating circuit I, and thisgating circuit has an output 162 coupled to an input 164 of a counter166. Now, when the gating circuits I and II are enabled, the 10 MHzpulse train from crystal oscillator 124 passes through the gatingcircuit II to the high speed 24 bit counter 156, and 5 to 10 KHz signalon the differential line receiver output 158 passes through the gratingcircuit I to the counter 166.

As seen in FIG. 4B, there is provided a conword II circuit 168, whichincludes logic circuitry and has an input 170 for receiving informationfrom the computer 76 indicating the number of periods, outputted by thedifferential line receiver 122, to be measured, i.e 4000, 2000, 1000, or500. .[.As.]. .Iadd.An .Iaddend.output 172 of the conword II circuit 168is coupled to an input 174 of a binary comparator 176. A second input178 couples the comparator to an output 180 of the counter 166. It willbe appreciated that the conword I and II circuits 132, 168 havepreviously been programmed by the computer according to the ratio of themaximum feed rate to the desired feed rate of the feeder assembly 10. Afeeder assembly with a high desired feed rate will have a relativelylarge change in weight per unit of time and, once the rate iscontrolled, a large change in the rate of change of the pulse trainfrequency outputted from the voltage to frequency converter 110. Thisenables measurements to be made more rapidly according to the followingschedule:

    __________________________________________________________________________                      NUMBER OF                                                                     PERIODS           RESULTANT TIME                                 MAX. FEED RATE                                                                             MEASURE  TIME BASE                                                                              REQUIRED FOR                              RATIO                                                                              DESIRED FEED RATE                                                                          (CONWORD II)                                                                           (CONWORD I)                                                                            MEASUREMENT                               __________________________________________________________________________    1 TO 2             500     .125 sec.                                                                              0.05-0.1 sec.*                            2 TO 4            1000     .250 sec.                                                                              0.1-0.2 sec.*                             4 TO 8            2000     .500 sec.                                                                              0.2-0.4 sec.*                             8 AND ABOVE       4000     1.000 sec.                                                                             0.4-0.8 sec.*                             __________________________________________________________________________     *Depends on frequency of pulse train.                                    

Thus, the number of periods designated by Conword II fixes the number ofperiods that go through gate I, i.e. the number of periods determinesthe gate cycle. The time base (Conword I) starts the operation of thegates, such as every 0.125 seconds, for example. The resultant time ittakes to get n periods, such as 500 for example, through gate I is, forexample, 0.05 seconds when the frequency of the voltage to frequencyconverter 110 is 10 KHz and 0.1 seconds when the frequency of thevoltage to frequency converter is 5 KHz.

The comparator 176 has an output 182, which is coupled to an input 184of a two phase one shot 186, having a first output 188 and a secondoutput 190. The first output 188 is coupled to an input 192 of a 24 bitdata latch or register 194. The second output 190 of the one shot isconnected to an input 196 of the high speed 24 bit counter 156 and isalso coupled to an input 198 of the counter 166. The output 182 of thebinary comparator 176 is also coupled to an input 200 of the gatingcircuit I and to an input 202 of the gating circuit II.

In operation, the counter 166 outputs the number of pulses counted tothe comparator 176 and when the comparator indicates that the number ofpulses counted equals the preselected number, as indicated by theconword II circuit 168, it outputs a signal from its output 182 to thetwo phase one shot 186 which, in turn, signals the 24 bit data latch 194to receive 24 bits of data from the high speed 24 bit counter 156 whichis coupled thereto as by coupling 204. The second output 190 of the twophase one shot applies a signal at 196 to clear and reset the high speed24 bit counter 156 and a signal at 198 to clear and reset the counter166. At the same time the output 182 of the binary comparator 176outputs a signal to the input 200 of the gating circuit I and the input202 of the gating circuit II, to open and reset these circuits. Thesecircuits now await the start of a new time base generator output. Inaddition, the output 182 outputs a signal via one shot 183 to thecomputer 76, indicating that the data is ready.

Meanwhile, the computer 76 has a minimum of 75 milliseconds in which torespond to the data ready signal. Still referring to FIG. 4B, the 24 bitdata latch 194 has an output 206 coupled to an input 208 of amultiplexer 210. The multiplexer also has an input 212 coupled toconword III circuit 214, that receives signals from the computer 76indicating the timing and sequence in which the three 8 bit groups ofthe 24 bit latch will be selected to be outputted by the multiplexer 210on the line 216 to the computer for processing in conjunction with thetime base information furnished by line 141.

When the time base generator 130 initiates a new period, the foregoingsequence is repeated.

A binary number system is employed as the code for information handlingbecause of certain advantages hereinafter brought out. Thus, the weighfeeder system is provided with a digital computer 76, which includesprocessing, memory and control systems. Any suitable digital computermay be employed such as a micro processor Model IMP16C/300 and memoryModel IMP16P/004P, as manufactured by National Semiconductor Corp., oran LSI-11 as manufactured by Digital Equipment Corp., for example.

As best seen in FIG. 5, a plurality of inputs are applied to theprocessor to control the same. A conventional off-on switch 218 servesto control the main power supply to the processor. A switch 220 isprovided whereby the refill sequence may be automatically actuated(switch in "auto") when product level reaches low level, or at anyproduct level (switch in "manual"), or the refill sequence may bebypassed (when switch is in "bypass"). The refill sequence is aprocedure wherein the motor speed will not lockout for refill, therebyactuating the refill controller, until the computer first senses thatthe scale is undisturbed by foreign influences and secondly, senses thatthe feed rate agrees with the set feed rate. Input switch 222 serves toconvert the system between gravimetric control and volumetric control,as desired. This will be explained more fully hereinafter. A reset totalpush button switch 224 serves to reset the processor for an entirely newbatch of data. Also, there is provided a scale weight switch 226, thatinputs into the processor the scale weight, S, which is determined bythe size or model of the feeder assembly 10 being employed in theparticular installation. This factor is set once and is not adjustedunless a new model or size of feeder assembly is installed.

A motor speed input switch 228 is provided, which is set by theoperators at a preselected percent in the range between 0% to 100%, toinput into the processor the desired operating speed of the motor whenoperating volumetrically.

Input switch 230 is actuated by the operator to input the desired feedrate R (LBS./HR) into the processor. This is a digital word, stored inmemory, that represents the desired slope of the feed line, which forthe embodiment illustrated in FIG. 1 is indicated by curve 232, FIG. 7,for example. Input switch 234 is also actuated by the operator to inputthe under weight set point into the processor memory. It represents theselected minimum limit of the feed rate range, as is indicated by thedotted line 236 in FIG. 7. This limit is expressed as a percentage offrom 0 to 9.99% below the desired feed rate R. Input switch 238 inputsthe overweight set point into memory. It represents the selected maximumlimit of the feed range, as is indicated by the dotted line 240 in FIG.7. This limit also is expressed as a percentage of from 0 to 9.99% abovethe desired feed rate R.

Still referring to FIG. 5, digital switch 242 is an operator activatedswitch to input into the memory, the desired minimum or low level of thematerial in the container 12, FIG. 1, or container 28, FIG. 2, orcontainer 46, FIG. 3. The range of this switch is from 0 to 99.9%. Thus,for example, if the operator desires the system to shift into its refillmode when the container 12 or 28 or 46 is down to 5% of its capacity, hesets the low level switch 242 at 05.0%. Digital input switch 244 is anout of low level switch with a range of from 0 to 99.9% so that theoperator can input into memory the desired level for the system to shiftout of its refill mode to its normal operative mode. Thus, for example,the operator could set this switch for 90.0%, whereby when the container12 or 28 or 46 reaches 90% of its capacity, the system would shift outof its refill mode to its normal operative mode.

In addition, the processor also receives a signal from a shaft encoder246, FIGS. 1-3. This allows a correlation to be made between the shaftangle and system noise induced by the movement of the material andmachinery mounted on the scale or, in the case of FIG. 1, the movementof the product in the storage hopper. This correlation may then be usedas a correction factor, subtracting out noise components due to movingmachinery on the scale such as for example, the motor, gear box, augers,as well as movement of the material in the container. The processor 76is provided with a learn mode input switch 248, which is shiftablebetween normal operation and learn mode operation. When a new materialis going to be processed by the system or when the system is firstinstalled, the system is set in operation, but instead of dischargingthe substance 14, FIG. 1, out of the system, it is collected in a smallcontainer, not shown, and retained on the scale 22 so that there is nonet loss of weight from the scale. The switch 248 is shifted to itslearn mode position. The motor 18 is run throughout its speed range andthe shaft encoder 246 senses the shaft angle, while the input circuit tothe computer 76, including the LVDT, picks up the noise corresponding tothe rotational position of the drive shaft and sends out digital signalsto the processor, which are stored in memory. After this information hasbeen stored in memory, the small container is removed from the scale andthe switch 248 is shifted to its normal operation. This same techniqueis applicable to the feeder assemblies of FIGS. 2 and 3, using acontainer on the respective scales to receive the material beingdischarged.

FIG. 8 illustrates the positional relationship of the shaft encoder 246with respect to the system noise detected for a particular shaft speedduring the learn mode operation. FIG. 9 illustrates the output of thevoltage to frequency converter 110 with respect to time, before it iscorrected for the induced system noise. Processor 76, as anotheroperation thereof, subtracts the stored system noise data from the datareceived from the voltage to frequency converter, through themultiplexer 210, to present connected values of this information forprocessing. FIG. 10 illustrates the corrected output from the voltage tofrequency converter 110 with respect to time. Any suitable type of shaftencoder may be employed such as a Series 2500, Optical Encoder, asmanufactured by Renco Corporation.

The microprocessor 76 has, as an output, a display device 250 whichindicates the total feed commanded. This device indicates the total feedasked for by the operator over a relatively long period of time. Thus,the processor, as one operation thereof, receives the selected feed rateR from the input switch 230 and integrates it with respect to theelapsed time and continuously displays the total feed commanded, inpounds. As another output there is provided a display device 252 whichindicates the actual total feed discharged from the feeder assembly 10.Thus, the processor, as one operation thereof, receives a signal fromthe multiplexer 210 corresponding to the total scale weight, which, inthe FIG. 1 apparatus, indicates the quantity of material remaining inthe container. This signal represents the weight of the material in thebin 12. Any change in this signal, except during refill, represents theamount of material fed. These changes are totalled by the processor togive the actual total feed, in pounds. During refill, in the FIG. 1apparatus, the amount of material fed is computed by the processor fromthe reading of the feed rate meter and the time it takes to refill. Whenrefill is completed the signal from the multiplexer 210 is again used tocompute the total amount of material fed. In the FIG. 2 and FIG. 3apparatus the total feed discharged can be determined directly from themeasured weight of the material being delivered. The operators cancompare the actual total feed, as displayed at 252, with the total feedcommanded, as displayed at 250, to determine how the system isfunctioning and, if necessary, take corrective action.

A feed rate display device, such as a four digit meter, 254, forexample, shows the actual feed rate in pounds per hour of the feederassembly. Thus, the processor, as another operation thereof, receivesthe scale weight signal from the multiplexer 210 and corrects thissignal, as pointed out hereinbefore, and then differentiates the signalwith respect to time to produce a signal indicative of the present rateof feed. This can be visually compared to the desired feed rate as setby the input switch 230 to determine possible malfunctions in thesystem.

A scale weight display device, such as a three digit meter 256, forexample, is provided to indicate the actual percentage of productremaining in the container 12 on the scale 22 of FIG. 1. Thus, theprocessor, as still another operation thereof, receives a signal fromthe multiplexer 210 corresponding to the weight on the scale 22 andcomputes the actual percentage of material remaining in the container12. Next, there is provided, as another output of the processor 76, athree digit motor speed meter 258 which indicates the actual speed ofthe motor 18. That is, the processor receives a signal from a tachometer260, indicating the speed of the motor 18, by a conductor 262 through aconventional analog-digital converter 264, and outputs a motor speed onmeter 258. While this speed is usually relatively constant, it may varyto some extent over a long period of time. It is advantageous for theoperator to know, as any sudden variations may indicate a blockage ofmaterial in the system.

In addition, there are provided operational and warning indicators, suchas lights, buzzers, or the like, for example, for purposes of keepingthe operators informed. An underweight light 266 indicates when theactual feed rate, as indicated by the meter 254, falls below theunderweight set point 234, and overweight light 268 indicates when theactual feed rate exceeds the overweight set point 238. That is, when theactual feed rate falls below the line 236, FIG. 7, which is set by theunderweight set point switch 234, the underweight light 266 is actuated,and when the actual feed rate is above the line 240, FIG. 7, which isset by the overweight set point switch 238, the overweight light 268 isactuated. Preferably, there is a preselected time delay period of fromabout 0 to about 3 minutes delay after the feed rate meter 254 indicatesan overweight or an underweight condition before the warning lights areactuated. Light 270 shows when the system is in its refill mode, i.e.when the container 12 is being refilled. The light 272 indicates thatthe system is in its ACRILOK mode. This mode of operation will beexplained more fully hereinafter. Run light 274 indicates that thesystem is in operation and standby light 276 indicates that the systempower has been applied, but all machinery is stopped. The light 278indicates that the bin 12 is in its low level condition.

A control output 280 from the processor 76 is applied to adigital-analog converter (DAC) 282. Any suitable type of DAC may beemployed, such as a 10 bit Model AD7520L, as manufactured by AnalogDevices, Inc., for example. In the DAC, the digital word is converted toan analog signal, which is applied to the tachometer 260 and an SCRmotor control 284. Any suitable type of motor control may be employedsuch as Acrison, Inc.'s Model ACR100BTG, for example. This controllerproduces an output which is applied to the motor 18 to control the speedthereof, and thereby control the discharge rate of the material from thefeeder assembly 10.

In operation, the operator must determine whether he wishes to operatein the volumetric mode or the gravimetric mode. If the volumetric modeis selected, then the operator sets the motor speed switch 228 to thedesired motor speed. In this mode of operation, the output of theprocessor is a digital word conveyed by conductor 280 to the DAC 282.The DAC causes a voltage from 0 to 6 volts to appear on conductor 286and the SCR motor control adjusts the speed of the DC motor 18 until theoutput of the tachometer 260 exactly equals the voltage on the conductor286. While this mode of operation is desirable at certain times, it doesnot provide as high a degree of accuracy as the gravimetric mode and,consequently, the gravimetric mode is predominantly employed.

In operation, when employing the embodiment of FIG. 1, when the operatorsets the switch 222 to the gravimetric mode of operation, the operatorthen sets the feed rate switch 230 to the desired feed rate R(LBS./HR.), which, as discussed hereinbefore, determines, the slope ofthe feed curve or line 232, FIG. 7. Samples are taken and stored in thecomputer memory. The samples, generally illustrated in FIG. 7 by dots,form the actual feed curve 288. It is noted that for each point orsample the gating circuits I and II open and close. The computer hasprogrammed therein a calculation time cycle, during which cycle thecomputer receives and stores a number of samples. The calculation timecycle, as well as the number of samples taken during such a cycle is afunction of the feed rate of the machine. For example, if the machinehas a high feed rate four samples may be taken for each calculation timecycle and if the machine has a low feed rate sixty samples may be takenfor each calculation time cycle. The calculation time cycle may rangefrom about 1/2 second to about 60 seconds, for example, depending on thefeed rate. Once during each calculation time cycle the processorcomputes a regression on these samples with respect to time, and thencecomputes the RMS error of the slope.

FIG. 7 illustrates an upper 3 RMS error line at 290 and a lower 3 RMSerror line at 292. If less than two, for example, sample data pointsexceed 3 RMS error in either direction, as indicated at 294 in FIG. 7,regression on time is recomputed with the data points exceeding 3 RMS,as indicated at 296, excluded. Thence, the computed slope of the actualfeed curve is compared with the slope of the desired or set point feedline, and a corresponding correction command is outputted at 280 toadjust the motor control 284, thereby to adjust the actual rate ofdischarge of the material from the feeder assembly 10. This calculationtime cycle is continuously repeated to continuously adjust the motorcontrol 284.

If more than two, for example, sample data points exceed 3 RMS error ineither direction, as indicated at 298 in FIG. 7, the system is changedinto its ACRILOK mode. That is, the ACRILOK light 272 is energized andthe output command 280 to the DAC 282 and motor control 284 is notupdated, but continues in its present state. That is, the processorcontinues to receive sample signals from the multiplexer 210 andcomputes the regression analysis thereof, but no correction command isoutputted at 280. The feed rate meter 254 is also locked at the lastcontrol data point. The feed system remains in a locked condition untila subsequent calculation time cycle of operation .Iadd.in which.Iaddend.less than two data points exceed 3 RMS error, and then thesystem is returned to its normal operating mode and the correctioncommand is again outputted at 280.

In the alternative, as illustrated in FIG. 11, the computer may beprogrammed in a second manner for outputting correction commands at 280to adjust the motor control 284. In operation, the operator sets thefeed rate switch 230, FIG. 5, to the desired feed rate R (LBS./HR.)which, as discussed hereinbefore, determines the slope of the desiredfeed curve or line 306, FIG. 11. As pointed out in connection with thecomputer program illustrated in FIG. 7, samples are taken and stored inthe computer memory. The samples, generally illustrated in FIG. 11 bydots 307, form the actual feed curve in segments, as indicated at 308,310, 312, 314 and 316. It is noted that for each point or sample thegating circuits I and II open and close. As pointed out hereinbefore,the computer has programmed therein a calculation time cycle, duringwhich cycle the computer receives and stores a number of samples. Thecalculation time cycle, as well as the number of samples taken duringsuch a cycle, is a function of the feed rate of the machine. Forexample, if the machine has a high feed rate four samples may be takenfor each calculation time cycle and if the machine has a low feed ratesixty samples may be taken for each time cycle. In FIG. 11 eight samplesare shown for each calculation time cycle, for example. The calculationtime cycle may range from about 1/2 second to about 60 seconds, forexample, depending on the feed rate. Once during each calculation timecycle the processor computes a regression on these samples with respectto time to determine the slope of the actual feed line during suchcalculation time cycle. The slope of one calculated time period orsegment is compared to the last derived slope to determine the deviationthereof. Thus, the percentage variation of the slope of segment 310 iscompared to that of segment 308. If the variation is within anacceptable range, then the slope is adjustable, and a correspondingcorrection command is outputted at 280 of the computer to adjust themotor control 284, thereby to adjust the actual rate of discharge of thematerial from the feeder assembly 10. The aforesaid acceptable range ispredetermined and it may be constant or it may be variable. As anexample, it may be within about 5 to 10% of the absolute value. However,if the percentage variation of the slope segment, such as that indicatedfor segment 312, is beyond the acceptable range, the system is changedinto its ACRILOK mode. That is, the ACRILOK light 272 is energized andthe output command 280 to the DAC 282 and motor control 284 is notupdated, but continues in its present state. Thus, the processorcontinues to receive sample signals from the multiplexer 210 and computethe regression analysis thereof, but no correction command is outputtedat 280. The feed rate meter 254 is also locked at the last control datapoint. The feed system remains in a locked condition until in asubsequent calculation time cycle of operation the variation of theslope is within an acceptable range, and then the system is returned toits normal operating mode and the correction command is again outputtedat 280.

As indicated above, the embodiment of FIG. 1 is a weight loss systemwherein the weight on the scale as sensed by the LVDT graduallydiminishes until the container 12 is empty. On the other hand, in theembodiments of FIGS. 2 and 3, the weight on the scale as sensed by theLVDT remains substantially constant. Thus, the output of the voltage tofrequency converter 110 is also substantially constant at somefrequency, such as 6 KHz., for example. That is, if the frequencyoutputted from the voltage to frequency converter 110 is constant at 5KHz. then the rate of flow is zero, and if the frequency is 10 KHz,there would be maximum or full flow of the machine. The computerreceives signals from the multiplexer 210 corresponding to the output ofthe voltage to frequency converter 110 in the same manner as thatdescribed hereinbefore. FIG. 12 illustrates the manner in which thecomputer is programmed for this mode of operation. In this mode ofoperation, the desired feed curve 318 is a straight horizontal line.Samples as indicated by dots 320 are taken and stored in the computermemory in the same manner as that described hereinbefore in connectionwith the mode of operation of FIG. 11. Thus, the samples form the actualfeed curve in segments, as indicated at 322, 324, 326, 328 and 330. Asindicated before, once during each calculation time cycle the processorcomputes a regression on these samples with respect to time to determinethe slope of the actual feed line during such calculation time periodcycle. The slope of one calculation time period or segment is comparedto the last derived slope to determine the deviation thereof. Thus, theslope of segment 324 is compared to that of segment 322, and if thevariation is within an acceptable range, then the slope is adjustable,and a corresponding correction command is outputted at 280 of thecomputer to adjust the motor control 284, thereby to adjust the actualrate of discharge of the material from the feeder assembly 10. Theaforesaid acceptable range is predetermined as described above inconnection with FIG. 11. If the percentage variation of the slopesegment such as that indicated for segment 328, is beyond the acceptablerange, the system is changed into its ACRILOK mode. As before, thesystem remains in the ACRILOK mode until in a subsequent calculationtime cycle of operation the variation of the slope is within anacceptable range of the last slope that was acceptable, and then thesystem is returned to its normal operating mode and the correctioncommand is again outputted at 280.

As still another operation of the processor, the total feed commanded,as indicated at 250, is compared to the actual total feed, as indicatedat 252, periodically, such as every 5 to 10 minutes, for example. Ifthere is a deviation exceeding predetermined limits, the processormodifies the aforementioned command output at 280 to gradually correctthe actual feed to the total feed. This is programmed to take from about5 minutes to about 10 minutes, thereby to avoid sharp fluctuations inthe feed rate command, but nevertheless, obtain as close as possible thetotal feed selected over a long period of time. This is, in effect, anoverride command and modifies the correction command, describedhereinbefore, as outputted at 280 of the computer. It is applicable toall of the gravimetric modes of operation described above, including theembodiments of FIGS. 1, 2 and 3.

A further operation of the processor, in the embodiment of FIG. 1, is todetermine when the scale weight, as indicated by the meter 256, drops toa predetermined low level, as set by the low level switch 242, and thensearch for an "on rate" condition. In the embodiments of FIGS. 2 and 3 asensor 299 is provided for sensing the level of the material in thecontainers 28 and 46, respectively, and when the level thereof drops toa predetermined low level, as set by the low level switch 242, theprocessor searches for an "on rate" condition. That is, the outputsignal outputted as 254 is monitored until the difference between it andthe feed rate switch 230 is less than a predetermined error limit.Thence, the system is changed into its refill mode wherein the outputcommand 280 and feed rate meter 254 are not updated, but are retained intheir present state, similar to their operation as describedhereinbefore in connection with the ACRILOK mode. At the same time, acommand is outputted to a refill circuit 300, which sends a signal to arefill controller 302 that controls the flow of material from a refillsource 304 to the container 12, FIG. 1, container 28, FIG. 2, andcontainer 46, FIG. 3. The controller 302 could be an AC motor whenhandling dry particulate material or could be a value when handlingliquids.

The system remains in the refill mode until, in the embodiment of FIG.1, the processor detects that the container 12 is refilled, as indicatedby the scale weight meter 256, and as selected by the out of low levelswitch 244. In the embodiments of FIGS. 2 and 3, the sensor 299 detectswhen the containers 28 and 46 are refilled to the extent, as selected bythe out of low level switch 244. At this time, the processor outputs asignal to the refill circuit 300 which, in turn, directs the refillcontroller 302 to discontinue refilling the container 12, FIG. 1,container 28, FIG. 2, and container 46, FIG. 3. The processor thenreturns the system to its normal operational mode.

FIGS. 13 to 19 are flow charts of the computer 76. Thus, FIG. 13 is aflow chart showing the program start, and FIG. 14 is a flow chart of thebackground routine. FIG. 15 is a flow chart of the timer routine andFIG. 16 shows the keyboard interrupts. FIG. 17 is a flow chart of thecalculation routine, and FIG. 18 computes the scale weight and hopperlevels, while FIG. 19 gives the subroutine description. Appendix A is aprogram with descriptive comments for carrying out the basic operationsof the computer 76.

From the foregoing disclosure, it can be seen that the instant inventionprovides an improved weigh feeding apparatus, wherein the discharge rateof a substance from a container may be maintained at a preselectedconstant value, wherein the container may be automatically refilledduring the continuous discharge of the substance, wherein excessiveexcursions of the system are eliminated, wherein extraneous datarecordings are eliminated when calculating the flow rate, and whereinpast flow rate values may be stored in memory and compensated for at alater point in time.

Although certain particular embodiments of the invention have beenherein disclosed for purposes of explanation, various modificationsthereof, after study of the specification, will be apparent to thoseskilled in the art to which the invention pertains.

What is claimed is: .[.1. A weigh feeding machine comprising a containerfor a substance; one preceding control electrical signal..].
 4. A weighfeeding machine comprising a container for a substance;discharge meansfor discharging the substance from the container at a controllablefeed-out rate; storage means for storing a first electrical signalcorresponding to the desired feed-out rate; means for sensing the weightof at least the substance in the container and for producing a secondelectrical signal at a frequency which corresponds to the value of saidweight and changes for the different values of weight sensed; means forsampling the second electrical signal during each of a succession oftime intervals; digital circuit means for comparing an electrical signalderived from said sampling of said second electrical signal with anelectrical signal derived from said first electrical signal, forproducing, as a result of said comparisons, control electrical signalsindicative of the desired changes, if any, in the feed-out rate of thedischarge means; control means for controlling the discharging means inaccordance with said control electrical signal to thereby maintain thefeed-out of the substance from the container at the desired feed-outrate; means for comparing a signal derived from at least one sampletaken during one of said time intervals with a signal derived from atleast one sample taken during another of said time intervals, forrepeating said comparison for successive time intervals, so that thesignal derived during each of said successive time intervals is comparedwith a signal derived during a different time interval, and forinhibiting the action of the control electrical signals on the controlmeans when said comparison shows a difference between the comparedsignals beyond a predetermined limit. .[. A weigh feeding machinecomprising a container for a substance;discharge means for dischargingthe substance from the container at a controllable feed-out rate; meansfor producing a first electrical signal corresponding to the desiredfeed-out rate; means for sensing the weight of at least the substance inthe container and for producing a second electrical signal proportionalto the value of said weight; digital circuit means for comparing anelectrical signal derived from said sampling of said second electricalsignal with an electrical signal derived from the first electricalsignal, for producing, as a result of said comparison, a controlelectrical signal indicative of the desired changes, if any, in thefeed-out rate of the discharge means; control means for controlling thedischarging means in accordance with said control electrical signal tothereby maintain the feed-out of the substance from the container at thedesired feed-out rate; means for comparing a signal derived from saidsecond electrical signal during each of a succession of time intervalswith a signal derived from said second electrical signal during adifferent one of said time intervals; and means, responsive to saidcomparisons of signals derived from said second electrical signalsduring successive time intervals, for inhibiting the control means whensaid comparison shows a difference between the compared signals beyond apredetermined limit and for establishing a feed-out rate correspondingto the value of at least one preceding control electrical signal..]..[.6. A weigh feeding machine according to claim 5 wherein said samplingand comparing means compares a signal derived from at least one sampletaken during each time interval with a signal derived from at least onesample taken during the immediately preceding time interval..].
 7. Aweigh feeding machine comprising a container for a substance;dischargemeans for discharging the substance from the container at a controllablefeed-out rate; storage means for storing a first electrical signalcorresponding to the desired feed-out rate; means for sensing the weightof the container and its contents and for producing a second electricalsignal at a frequency which corresponds to the value of said weight;digital circuit means for sampling the second electrical signal duringeach of a succession of time intervals; storage means for storing thefrequency signals representative of the samples of said secondelectrical signal during such succession of time intervals; digitalcomputer means for computing a succession of feed-out rates from thefrequency signals corresponding to the samples taken during saidsuccessive time intervals, and for comparing an electrical signalrepresentative of each said computed feed-out rate with the firstelectrical signal representative of said desired feed-out rate, forproducing, as a result of said comparisons, control electrical signalsindicative of the desired changes, if any, in the feed-out rate of thedischarge means; control means for controlling the discharging means inaccordance with said control electrical signals to thereby maintain thefeed-out of the substance from the container at the desired feed-outrate; and means for comparing a signal derived from at least one sampletaken during one of said time intervals with a signal derived from atleast one sample taken during another of said time invervals, forrepeating said comparison for successive time intervals, so that thesignal derived during each of said successive time intervals is comparedwith a signal derived during a different time interval, and forinhibiting the action of the control electrical signal on the controlmeans when said comparison shows a difference between the comparedsignals beyond a predetermined limit.
 8. A weigh feeding machinecomprising a container for a substance;discharge means for dischargingthe substance from the container at a controllable feed-out rate;storage means for storing a first electrical signal corresponding to thedesired feed-out rate; means for sensing the weight of the substancedischarged from the container and for producing a second electricalsignal at a frequency which corresponds to the instantaneous value ofsaid weight; digital circuit means for sampling the second electricalsignal during each of a succession of time intervals; storage means forstoring the frequency signals representative of the samples of saidsecond electrical signal; digital circuit means for comparing electricalsignals derived from said sampling of said second electrical signal withan electrical signal derived from the first electrical signal, forproducing, as a result of said comparison, a control electrical signalindicative of the desired changes, if any, in the feed-out rate of thedischarge means; control means for controlling the discharging means inaccordance with said control electrical signal to thereby maintain thefeed-out of the substance from the container at the desired feed-outrate; means for comparing a signal derived from samples taken duringeach of a succession of said time intervals with a signal derived fromsaid second electrical signal during a different one of said timeintervals; and means, responsive to the last-mentioned comparisons, forinhibiting the control means when said comparison shows a differencebetween the compared signals beyond a predetermined limit and forestablishing a feed-out rate corresponding to the value of a least onepreceding control electrical signal.
 9. A weigh feeding machinecomprising a container for a substance;discharge means for dischargingthe substance from the container at a controllable feed-out rate;storage means for storing a first electrical signal corresponding to thedesired feed-out rate; means for sensing the weight of at least thesubstance in the container and for producing a second electrical signalat a frequency which corresponds to the value of said weight and changesfor the different values of weight sensed; digital circuit means forsampling the second electrical signal successively, each samplingincluding a predetermined number of periods of said second electricalsignal; said digital circuit means sampling said second electricalsignal a plurality of times during each of a succession of timeintervals; storage means for storing the samples of said secondelectrical signal during each such time interval; digital computer meansfor computing a feed-out rate during each such time interval, from thesamples taken during such time interval, and for comparing an electricalsignal representative of said computed feed-out rate with the firstelectrical signal representative of said desired feed-out rate, forproducing, as a result of said comparison, a control electrical signalindicative of the desired changes, if any, in the feed-out rate of thedischarge means; control means for controlling the discharging means inaccordance with said control electrical signal to thereby maintain thefeed-out of the substance from the container at the desired feed-outrate; and means for comparing a signal derived from at least one sampletaken during one of said time intervals with a signal derived from atleast one sample taken during another of said time intervals, forrepeating said comparison for successive time intervals, so that thesignal derived during each of said successive time intervals is comparedwith a signal derived during a different time interval, and forinhibiting the action of the control electrical signal on the controlmeans when said comparison shows a difference between the comparedsignals beyond a predetermined limit.
 10. A weigh feeding machineaccording to claim 9, wherein,during each sampling, said digital circuitmeans samples said second electrical signal for a number of periods ofsaid second signal which varies inversely with the value of the desiredfeed-out rate.
 11. A weigh feeding machine according to claim 9,wherein,during each time interval, said digital circuit means samplessaid second electrical signal a number of times which varies inverselywith the desired feed-out rate.
 12. A weigh feeding machine according toclaim 9, whereinsaid means for comparing compares the signalrepresentative of the computed feed-out rate for each time interval withthe signal representative of the computed feed-out rate for at least onepreceding time interval.
 13. A weigh feeding machine according to claim.[.9.]. .Iadd.12.Iaddend., wherein the comparison means for the computedfeed-out rate compares the signal representative of each computedfeed-out rate with the signal representative of the computed feed-outrate for the immediately preceding time interval.
 14. A weigh feedingmachine according to claim .[.9.]. .Iadd.12.Iaddend., wherein, when thecomparison between the signals for the computed feed-out rates fordifferent time intervals is beyond said predetermined limit, saidinhibiting means inhibits any control electrical signal from beingtransmitted to the control means, so that the feed-out rate continues atthe rate to which it was last corrected.
 15. A weigh feeding machineaccording to claim 9, wherein,the digital circuit means includes a highfrequency oscillator having an operating frequency at least an order ofmagnitude higher than the frequency corresponding to the value of theweight being sensed; gating means coupled to said high frequencyoscillator; and second control means for enabling said gating means fora period of time corresponding to a predetermined number of periods ofthe frequency corresponding to the weight being sensed, to pass signalsfrom said high frequency oscillator during said period of time, tothereby convert the frequency of the weight being sensed to said highfrequency.
 16. A weigh feeding machine according to claim 15, whereinsaid second control means enables the gating means for a predeterminednumber of periods which varies inversely with the value of the desiredfeed-out rate.
 17. A weigh feeding machine according to claim 15,further includingstorage means for storing the signals from said highfrequency oscillator; and multiplexing means coupled to said storagemeans for multiplexing the different portions of the high frequencysignal out of said storage means in a predetermined sequence.
 18. Aweigh feeding machine according to claim 15, whereinsaid gating meansincludes a first gating means for the low frequency second electricalsignal and a second gating means for the high .Iadd.frequency.Iaddend.electrical signal from said oscillator; and said second controlmeans enables said first and second gating means simultaneously; furtherincludinga first counter coupled to said first gating means for countingthe periods of said low frequency second electrical signal, a secondcounter coupled to said second gating means for counting the periods ofsaid high frequency electrical signal, and disabling means responsive tosaid first counter reaching a predetermined count for disabling saidsecond gating means.
 19. A weigh feeding machine according to claim 18,wherein said disabling means includes a comparison circuit coupled tosaid first counter for producing a disabling signal when said firstcounter has reached a predetermined count, for disabling said first andsecond gating means.
 20. A weigh feeding machine comprising a containerfor a substance;discharge means for discharging the substance from thecontainer at a controllable feed-out rate; storage means for storing afirst electrical signal corresponding to the desired feed-out rate;means for sensing the weight of at least the substance in the containerand for producing a second electrical signal at a frequency whichcorresponds to the value of said weight and changes for the differentvalues of weight sensed; digital circuit means for sampling the secondelectrical signal a plurality of times during a predetermined timeinterval, for a succession of said time intervals; said digital circuitmeans including circuit means for converting the frequency of thesampled signal to a higher frequency which is at least an order ofmagnitude higher than the frequency of the sampled signal; storage meansfor storing the higher frequency signals representative of the samplesof said second electrical signal during each such time interval; digitalcomputer means for computing a feed-out rate during each such timeinterval, from the higher frequency signals corresponding to the samplestaken during one such time interval, and for comparing an electricalsignal representative of said computed feed-out rate with the firstelectrical signal representative of said desired feed-out rate, forproducing, as a result of said comparison, a control electrical signalindicative of the desired changes, if any, in the feed-out rate of thedischarge means; control means for controlling the discharging means inaccordance with said control electrical signal to thereby maintain thefeed-out of the substance from the container at the desired feed-outrate; and means for comparing the signal representative of the computedfeed-out rate for each such time interval with the signal representativeof the computed feed-out rate for at least one preceding time interval;and inhibiting means, responsive to said comparison of computed feed-outrates, for inhibiting the action of the control electrical signal on thecontrol means when said comparison shows a difference between thecomputed feed-out rates beyond a predetermined limit.
 21. A weighfeeding machine according to claim 20 wherein said digital circuit meanssamples said second electrical signal for a predetermined number of itsperiods during each sampling, and produces a larger number of periods atthe higher frequency extending over substantially the same timeduration.
 22. A weigh feeding maching according to claim 20, whereinsaid digital circuit means includes a high frequency oscillator havingan operating frequency at least an order of magnitude higher than thefrequency corresponding to the value of the weight being sensed;gatingmeans coupled to said high frequency oscillator; and second controlmeans for enabling said gating means for a period of time correspondingto a predetermined number of periods of the frequency corresponding tothe weight being sensed, to pass signals from said high frequencyoscillator during said period of time, to thereby convert the frequencyof the weight being sensed to said high frequency. .[.23. A weighfeeding machine comprising a container for a substance; discharge meansfor discharging the substance from the container at a controllablefeed-out rate; storage means for storing a first electrical signalcorresponding to the desired feed-out rate; means for sensing the weightof at least the substance in the container and for producing a secondelectrical signal having a characteristic which corresponds to the valueof said weight; said digital circuit means sampling said secondelectrical signal a plurality of times during each of a succession oftime intervals; storage means for storing the samples of said secondelectrical signal during each such time interval; digital computer meansfor computing a feed-out rate during each such time interval, from thesamples taken during one such time interval, and for comparing anelectrical signal representative of said computed feed-out rate with thefirst electrical signal representative of said desired feed-out rate,for producing, as a result of said comparison, a control electricalsignal indicative of the desired changes, if any, in the feed-out rateof the discharge means; control means for controlling the dischargingmeans in accordance with said control electrical signal to therebymaintain the feed-out of the substance from the container at the desiredfeed-out rate; and means for comparing a signal derived from at leastone sample taken during one of said time intervals with a signal derivedfrom at least one sample taken during another of said time intervals,for repeating said comparison for successive time intervals, so that thesignal derived during each of said successive time intervals is comparedwith a signal derived during a different time interval, and forinhibitng the action of the control electrical signal on the controlmeans when said comparison shows a difference between the comparedsignals beyond a predetermined limit..]. .[.24. A weigh feeding machineaccording to claim 23, wherein the means for comparing the signalsderived from samples taken in different time intervals compares thesignal representative of each computed feed-out rate with the signalrepresentative of the computed feed-out rate for the immediatelypreceding time interval..]. .[.25. A weigh feeding machine according toclaim 23, wherein, when comparison between the signals derived fromsamples taken in different time intervals is beyond said predeterminedlimit, said inhibiting means inhibits any control electrical signal frombeing transmitted to the control means, so that the feed-out ratecontinues at the rate to which it was last corrected..]. .[.26. A weighfeeding device comprisinga container for a substance; discharge meansfor discharging the substance from the container at a controllablefeed-out rate; storage means for storing a first electrical signalcorresponding to the desired feed-out rate; means for sensing the weightof at least the substance in the container; first circuit meansresponsive to said sensing means for producing a succession of secondelectrical signals, each at a frequency which is responsive to the valueof the weight sensed; counting means for counting the cycles of each ofsaid second electrical signals to produce a succession of total counts,each of which is a measure of the value of the weight sensed; a digitalcircuit for storing said total counts and comparing an electrical signalresponsive to a plurality of said total counts with the first electricalsignal representative of said desired feed-out rate, for producing, as aresult of said comparison, a control electrical signal indicative of thedesired changes, if any, in the feed-out rate of the discharge means;and control means for controlling the discharge means in accordance withsaid control electrical signal to thereby maintain the feed-out of thesubstance from the container at the desired feed-out rate..]. .[.27. Aweight feeding device according to claim 26, whereinsaid digital circuitincludes means for computing one or more error limits in the form ofdeviations from the computed feed-out rate; and means operative incomputing the feed-out rate, for excluding from the computation thereofany total count values which fall beyond said error limits..]. .[.28. Aweigh feeding device comprising a container for a substance; dischargemeans for discharging the substance from the container at a controllablefeed-out rate; storage means for storing a first electrical signalcorresponding to the desired feed-out rate; a voltage source forproducing an output voltage at a predetermined number of cycles persecond; means for sensing the weight of at least the substance in thecontainer and producing a second electrical signal responsive to saidweight; circuit means responsive to said second electrical signal forgating a succession of cycles of said output voltage from said voltagesource for a period of time, the duration of which is dependent upon thevalue of said weight; counting means for counting the cycles gated fromsaid source to produce a total count which is a measure of the value ofthe weight being sensed; a digital circuit for comparing an electricalsignal responsive to said total count with the first electrical signalrepresentative of said desired feed-out rate, for producing, as a resultof said comparison, a control electrical signal indicative of thedesired changes, if any, in the feed-out rate of the discharge means;and control means for controlling the discharge means in accordance withsaid control electrical signal to thereby maintain the feed-out of thesubstance from the container at the desired feed-out rate..].
 29. Aweigh feeding device .[.according to claim 28, wherein.]..Iadd.comprising a container for a substance; discharge means fordischarging the substance from the container at a controllable feed-outrate; storage means for storing a first electrical signal correspondingto the desired feed-out rate; a voltage source for producing an outputvoltage at a predetermined number of cycles per second; means forsensing the weight of at least the substance in the container andproducing a second electrical signal responsive to said weight; circuitmeans responsive to said second electrical signal for gating asuccession of cycles of said output voltage from said voltage source fora period of time, the duration of which is dependent upon the value ofsaid weight: .Iaddend.said circuit means includes sampling means forrepeatedly sampling the second electrical signal from said sensingmeans.[.;.]. .Iadd., .Iaddend. each such sample controlling the periodof time over which the output from said voltage source is gated;.[.said.]. counting means .Iadd.for .Iaddend.counting the cycles gatedfrom said source for each .Iadd.of .Iaddend.said .[.sampling andproducing.]. .Iadd.samplings to produce .Iaddend.a series of totalcounts, .[.one for.]. each of said .[.samplings;.]. .Iadd.total countsbeing a measure of the value of the weight being sensed during one ofsaid samplings .Iaddend. storage means for storing all of said totalcounts; and .[.said.]. .Iadd.a .Iaddend.digital circuit .Iadd.for.Iaddend.computing the feed-out rate from a plurality of .[.the.]..Iadd.said .Iaddend.total counts which occur during a predetermined timeinterval.Iadd., comparing an electrical signal responsive to saidfeed-out rate with the first electrical signal representative of saiddesired feed-out rate, and for producing, as a result of saidcomparison, a control electrical signal indicative of the desiredchanges, if any, in the feed-out rate of the discharge means; andcontrol means for controlling the discharge means in accordance withsaid control electrical signal to thereby maintain the feed-out of thesubstance from the container at the desired feed-out rate.Iaddend...[.30. A weigh feeding device comprising a container for a substance;discharge means for discharging the substance from the container at acontrollable feed-out rate; storage means for storing a first electricalsignal corresponding to the desired feed-out rate; means for sensing theweight of at least the substance in the container and for producing asecond electrical signal which corresponds to the value of said weight;a voltage source for producing an output signal at a predeterminedfrequency; counting means for counting the signals from said voltagesource; a digital circuit for sampling the second electrical signalsuccessively and, for each such sampling, gating output signals fromsaid voltage source to said counting means for a period of time whichcorresponds to a characteristic of said second electrical signal;storage means for storing a plurality of values corresponding to thetotal counts of said counting means for all of said samplings; digitalcomputer means for computing a feed-out rate from the total counts for aplurality of said samples, and for comparing an electrical signalrepresentative of said computed feed-out rate with the first electricalsignal representative of said desired feed-out rate, for producing, as aresult of said comparison, a control electrical signal indicative of thedesired changes, if any, in the feed-out rate of the discharge means;and control means for controlling the discharge means in accordance withsaid control electrical signal to thereby maintain the feed-out of thesubstance from the container at the desired feed-out rate..]. .[.31. Aweigh feeding device according to claim 30, further includingcircuitmeans controlled by said digital computer for initiating each successiveperiod of time for which output signals from said voltage source aregated to said counting means, and said digital circuit terminating eachsuch successive period of time at a time which corresponds to the valueof the characteristic of the second electrical signal..].
 32. A weighfeeding device comprisinga container for a substance; discharge meansfor discharging the substance from the container at a controllablefeed-out rate; means for establishing a first electrical signalcorresponding to the desired feed-out rate; source means for producingan output signal at a predetermined frequency; counting means coupled tosaid source means for receiving and counting the signals therefrom;means for sensing the weight of at least the substance in the containerand for producing a second electrical signal having a frequency whichcorresponds to the value of said weight; digital circuit means forrepeatedly sampling said second signal and controlling the count of saidcounting means, during each such sampling, to count .[.to.]. .Iadd.for atime dependent upon .Iaddend.the frequency of said second signal at thetime of said sampling; storage means for storing a plurality of values,each corresponding to the count of said counting means for one of saidsamplings; digital computer means for computing a feed-out rate for eachof a succession of time intervals, from the count samples during onesuch time interval, and for comparing an electrical signalrepresentative of said computed feed-out rate with the first electricalsignal representative of said desired feed-out rate, for producing, as aresult of said comparison, a control electrical signal indicative of thedesired changes, if any, in the feed-out rate of the discharge means;and control means for controlling the discharging means in accordancewith said control electrical signal to thereby maintain the feed-out ofthe substance from the container at the desired feed-out rate.
 33. Aweigh feeding device comprisinga container for a substance; dischargemeans for discharging the substance from the container at a controllablefeed-out rate; means for establishing a first electrical signalcorresponding to the desired feed-out rate; means for sensing the weightof at least the substance in the container and for producing a secondelectrical signal having a characteristic which corresponds to the valueof said weight; a source of signals at a predetermined frequency; acounter for counting the signals from said source; storage means forstoring a succession of values corresponding to counts of said counter;digital circuit means for sampling the second electrical signalsuccessively and for transmitting from said counter to said storagemeans, for each such sampling, a value corresponding to the count of thecounter for a period of time proportional to the weight sensed; digitalcomputer means for computing a feed-out rate from a plurality of saidcount values, and for comparing an electrical signal representative ofsaid computed feed-out rate with the first electrical signalrepresentative of said desired feed-out rate, for producing, as a resultof said comparison, a control electrical signal indicative of thedesired changes, if any, in the feed-out rate of the discharge means;and control means for controlling the discharge means in accordance withsaid control electrical signal to thereby maintain the feed-out of thesubstance from the container at the desired feed-out rate.
 34. A weighfeeding device according to claim 33 whereinthe sensing means producesan electrical signal whose frequency corresponds to the value of theweight being sensed; further including second counting means forcounting the signals from said sensing means; and means responsive tothe count in said second counting means for controlling said period oftime for said first counting means. .[.35. A weigh feeding machinecomprising a container for a substance; discharge means for dischargingthe substance from the container at a controllable feed-out rate; meansfor producing a first electrical signal corresponding to the desiredfeed-out rate; means for sensing the weight of at least the substance inthe container and for producing a second electrical signal having acharacteristic which is proportional to the value of said weight;digital circuit means for sampling said second electrical signal atleast once during each of a succession of time intervals; means forcomputing a feed-out rate during each of said time intervals fromsignals derived from said sampling and for comparing an electricalsignal representative of each such computed feed-out rate with the firstelectrical signal representative, for producing, as a result of saidcomparison, control electrical signals indicative of the desiredchanges, if any, in the feed-out rate of the discharge means; controlmeans for controlling the discharging means in accordance with saidcontrol electrical signals to thereby maintain the feed-out of thesubstance from the container at the desired feed-out rate; and means forcomparing a signal derived from at least one sample taken during one ofsaid time intervals with a signal derived from at least one sample takenduring another of said time intervals, for repeating said comparison forsuccessive time intervals, so that the signal derived during each ofsaid successive time intervals is compared with a signal derived duringa different time interval, and for inhibiting the action of the controlelectrical signal on the control means when said comparison shows adifference between the compared signals beyond a predetermined time..]..[.6. A weigh feeding machine according to claim 35,wherein the meansfor comparing the signals derived from samples taken in different timeintervals compares a signal representative of each computed feed-outrate with a signal representative of the computed feed-out rate for theimmediately preceding time interval..].